On Flames containing Vaporised Salts. 143 



in a flame. By some the liberation is supposed to be effected thermally 

 by chemical dissociation ; others suppose that the salt is converted into 

 hydrate or oxide, and then reduced by the flame gases. It is also note- 

 worthy that, however the metal be liberated, and however oxidisable it 

 may be, light is emitted from parts of the flame where oxidising gases 

 -are in abundance, and where even less oxidisable metals in the massive 

 state are rapidly oxidised. 



The primary object of the experiments described in this paper is to 

 ascertain whether the luminosity imparted by vaporised salts to flames 

 is related in a definite manner to the electrical conductivity of the salt 

 vapours. The conductivity of vaporised salts in flames has been in- 

 vestigated by Arrhenius,* who concluded that it was of an electrolytic 

 character. In the case of alkali salts, Arrhenius supposes that the 

 salt vapour is acted upon by the large quantity of water vapour in the 

 flame, in accordance with the following equation 





and that the metallic hydrate so formed undergoes partial electrolytic 



dissociation into the ions M and (HO). From the analogy stated to 

 exist between dilute solutions of solids and matter in the gaseous 

 state, and from his own theory that in dilute solutions electrolytes are 

 in greater or less degree dissociated into their ions, Arrhenius was led 

 to believe that electrolytes distributed in small concentration through- 

 out a gas, would likewise be electrolytically dissociated, a view to 

 which his results as above stated, are conformable. 



Since, according to the electrolytic dissociation theory of Arrhenius 

 -as applied to dilute solutions, the metallic ion in virtue of its electric 

 charge can persist in an oxidising medium, it appeared that if the 

 same theory were really applicable to salts vaporised in flames, it would 

 afford an explanation both of the liberation of the element, and of its 

 persistence in the midst of an oxidising atmosphere of flame gases. 



Another consideration appeared to favour this hypothesis. Accord- 

 ing to Arrhenius, the conductivity of a salt vapour is proportional to 

 the square root of its concentration in the flame, and according to 

 Gouyf the luminosity of a flame coloured by an alkali salt also follows 

 within certain limits, the same law. 



The motive of the present authors was to test the above hypothesis, 

 and incidentally to gain increased knowledge of the circumstances that 

 govern the electrical conductivity of vaporised salts. 



* ' Wied. Ann.,' vol. 42, p. 18, 1891. 



f Gouy, ' Ann. China. Phys.,' vol. 18, p. 5, 1879. 



